a9ee2c1176fe221b6eb3b2f9c5f74ae3d38cd835
[sfrench/cifs-2.6.git] / fs / overlayfs / readdir.c
1 /*
2  *
3  * Copyright (C) 2011 Novell Inc.
4  *
5  * This program is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License version 2 as published by
7  * the Free Software Foundation.
8  */
9
10 #include <linux/fs.h>
11 #include <linux/slab.h>
12 #include <linux/namei.h>
13 #include <linux/file.h>
14 #include <linux/xattr.h>
15 #include <linux/rbtree.h>
16 #include <linux/security.h>
17 #include <linux/cred.h>
18 #include "overlayfs.h"
19
20 struct ovl_cache_entry {
21         unsigned int len;
22         unsigned int type;
23         u64 ino;
24         bool is_whiteout;
25         struct list_head l_node;
26         struct rb_node node;
27         char name[];
28 };
29
30 struct ovl_dir_cache {
31         long refcount;
32         u64 version;
33         struct list_head entries;
34 };
35
36 struct ovl_readdir_data {
37         struct dir_context ctx;
38         bool is_merge;
39         struct rb_root root;
40         struct list_head *list;
41         struct list_head *middle;
42         int count;
43         int err;
44 };
45
46 struct ovl_dir_file {
47         bool is_real;
48         bool is_upper;
49         struct ovl_dir_cache *cache;
50         struct ovl_cache_entry cursor;
51         struct file *realfile;
52         struct file *upperfile;
53 };
54
55 static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n)
56 {
57         return container_of(n, struct ovl_cache_entry, node);
58 }
59
60 static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
61                                                     const char *name, int len)
62 {
63         struct rb_node *node = root->rb_node;
64         int cmp;
65
66         while (node) {
67                 struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
68
69                 cmp = strncmp(name, p->name, len);
70                 if (cmp > 0)
71                         node = p->node.rb_right;
72                 else if (cmp < 0 || len < p->len)
73                         node = p->node.rb_left;
74                 else
75                         return p;
76         }
77
78         return NULL;
79 }
80
81 static struct ovl_cache_entry *ovl_cache_entry_new(const char *name, int len,
82                                                    u64 ino, unsigned int d_type)
83 {
84         struct ovl_cache_entry *p;
85         size_t size = offsetof(struct ovl_cache_entry, name[len + 1]);
86
87         p = kmalloc(size, GFP_KERNEL);
88         if (p) {
89                 memcpy(p->name, name, len);
90                 p->name[len] = '\0';
91                 p->len = len;
92                 p->type = d_type;
93                 p->ino = ino;
94                 p->is_whiteout = false;
95         }
96
97         return p;
98 }
99
100 static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
101                                   const char *name, int len, u64 ino,
102                                   unsigned int d_type)
103 {
104         struct rb_node **newp = &rdd->root.rb_node;
105         struct rb_node *parent = NULL;
106         struct ovl_cache_entry *p;
107
108         while (*newp) {
109                 int cmp;
110                 struct ovl_cache_entry *tmp;
111
112                 parent = *newp;
113                 tmp = ovl_cache_entry_from_node(*newp);
114                 cmp = strncmp(name, tmp->name, len);
115                 if (cmp > 0)
116                         newp = &tmp->node.rb_right;
117                 else if (cmp < 0 || len < tmp->len)
118                         newp = &tmp->node.rb_left;
119                 else
120                         return 0;
121         }
122
123         p = ovl_cache_entry_new(name, len, ino, d_type);
124         if (p == NULL)
125                 return -ENOMEM;
126
127         list_add_tail(&p->l_node, rdd->list);
128         rb_link_node(&p->node, parent, newp);
129         rb_insert_color(&p->node, &rdd->root);
130
131         return 0;
132 }
133
134 static int ovl_fill_lower(struct ovl_readdir_data *rdd,
135                           const char *name, int namelen,
136                           loff_t offset, u64 ino, unsigned int d_type)
137 {
138         struct ovl_cache_entry *p;
139
140         p = ovl_cache_entry_find(&rdd->root, name, namelen);
141         if (p) {
142                 list_move_tail(&p->l_node, rdd->middle);
143         } else {
144                 p = ovl_cache_entry_new(name, namelen, ino, d_type);
145                 if (p == NULL)
146                         rdd->err = -ENOMEM;
147                 else
148                         list_add_tail(&p->l_node, rdd->middle);
149         }
150
151         return rdd->err;
152 }
153
154 void ovl_cache_free(struct list_head *list)
155 {
156         struct ovl_cache_entry *p;
157         struct ovl_cache_entry *n;
158
159         list_for_each_entry_safe(p, n, list, l_node)
160                 kfree(p);
161
162         INIT_LIST_HEAD(list);
163 }
164
165 static void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
166 {
167         struct ovl_dir_cache *cache = od->cache;
168
169         list_del(&od->cursor.l_node);
170         WARN_ON(cache->refcount <= 0);
171         cache->refcount--;
172         if (!cache->refcount) {
173                 if (ovl_dir_cache(dentry) == cache)
174                         ovl_set_dir_cache(dentry, NULL);
175
176                 ovl_cache_free(&cache->entries);
177                 kfree(cache);
178         }
179 }
180
181 static int ovl_fill_merge(void *buf, const char *name, int namelen,
182                           loff_t offset, u64 ino, unsigned int d_type)
183 {
184         struct ovl_readdir_data *rdd = buf;
185
186         rdd->count++;
187         if (!rdd->is_merge)
188                 return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
189         else
190                 return ovl_fill_lower(rdd, name, namelen, offset, ino, d_type);
191 }
192
193 static inline int ovl_dir_read(struct path *realpath,
194                                struct ovl_readdir_data *rdd)
195 {
196         struct file *realfile;
197         int err;
198
199         realfile = ovl_path_open(realpath, O_RDONLY | O_DIRECTORY);
200         if (IS_ERR(realfile))
201                 return PTR_ERR(realfile);
202
203         rdd->ctx.pos = 0;
204         do {
205                 rdd->count = 0;
206                 rdd->err = 0;
207                 err = iterate_dir(realfile, &rdd->ctx);
208                 if (err >= 0)
209                         err = rdd->err;
210         } while (!err && rdd->count);
211         fput(realfile);
212
213         return err;
214 }
215
216 static void ovl_dir_reset(struct file *file)
217 {
218         struct ovl_dir_file *od = file->private_data;
219         struct ovl_dir_cache *cache = od->cache;
220         struct dentry *dentry = file->f_path.dentry;
221         enum ovl_path_type type = ovl_path_type(dentry);
222
223         if (cache && ovl_dentry_version_get(dentry) != cache->version) {
224                 ovl_cache_put(od, dentry);
225                 od->cache = NULL;
226         }
227         WARN_ON(!od->is_real && type != OVL_PATH_MERGE);
228         if (od->is_real && type == OVL_PATH_MERGE)
229                 od->is_real = false;
230 }
231
232 static int ovl_dir_mark_whiteouts(struct dentry *dir,
233                                   struct ovl_readdir_data *rdd)
234 {
235         struct ovl_cache_entry *p;
236         struct dentry *dentry;
237         const struct cred *old_cred;
238         struct cred *override_cred;
239
240         override_cred = prepare_creds();
241         if (!override_cred) {
242                 ovl_cache_free(rdd->list);
243                 return -ENOMEM;
244         }
245
246         /*
247          * CAP_DAC_OVERRIDE for lookup
248          */
249         cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
250         old_cred = override_creds(override_cred);
251
252         mutex_lock(&dir->d_inode->i_mutex);
253         list_for_each_entry(p, rdd->list, l_node) {
254                 if (!p->name)
255                         continue;
256
257                 if (p->type != DT_CHR)
258                         continue;
259
260                 dentry = lookup_one_len(p->name, dir, p->len);
261                 if (IS_ERR(dentry))
262                         continue;
263
264                 p->is_whiteout = ovl_is_whiteout(dentry);
265                 dput(dentry);
266         }
267         mutex_unlock(&dir->d_inode->i_mutex);
268
269         revert_creds(old_cred);
270         put_cred(override_cred);
271
272         return 0;
273 }
274
275 static inline int ovl_dir_read_merged(struct path *upperpath,
276                                       struct path *lowerpath,
277                                       struct list_head *list)
278 {
279         int err;
280         struct list_head middle;
281         struct ovl_readdir_data rdd = {
282                 .ctx.actor = ovl_fill_merge,
283                 .list = list,
284                 .root = RB_ROOT,
285                 .is_merge = false,
286         };
287
288         if (upperpath->dentry) {
289                 err = ovl_dir_read(upperpath, &rdd);
290                 if (err)
291                         goto out;
292
293                 if (lowerpath->dentry) {
294                         err = ovl_dir_mark_whiteouts(upperpath->dentry, &rdd);
295                         if (err)
296                                 goto out;
297                 }
298         }
299         if (lowerpath->dentry) {
300                 /*
301                  * Insert lowerpath entries before upperpath ones, this allows
302                  * offsets to be reasonably constant
303                  */
304                 list_add(&middle, rdd.list);
305                 rdd.middle = &middle;
306                 rdd.is_merge = true;
307                 err = ovl_dir_read(lowerpath, &rdd);
308                 list_del(&middle);
309         }
310 out:
311         return err;
312
313 }
314
315 static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
316 {
317         struct ovl_cache_entry *p;
318         loff_t off = 0;
319
320         list_for_each_entry(p, &od->cache->entries, l_node) {
321                 if (!p->name)
322                         continue;
323                 if (off >= pos)
324                         break;
325                 off++;
326         }
327         list_move_tail(&od->cursor.l_node, &p->l_node);
328 }
329
330 static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
331 {
332         int res;
333         struct path lowerpath;
334         struct path upperpath;
335         struct ovl_dir_cache *cache;
336
337         cache = ovl_dir_cache(dentry);
338         if (cache && ovl_dentry_version_get(dentry) == cache->version) {
339                 cache->refcount++;
340                 return cache;
341         }
342         ovl_set_dir_cache(dentry, NULL);
343
344         cache = kzalloc(sizeof(struct ovl_dir_cache), GFP_KERNEL);
345         if (!cache)
346                 return ERR_PTR(-ENOMEM);
347
348         cache->refcount = 1;
349         INIT_LIST_HEAD(&cache->entries);
350
351         ovl_path_lower(dentry, &lowerpath);
352         ovl_path_upper(dentry, &upperpath);
353
354         res = ovl_dir_read_merged(&upperpath, &lowerpath, &cache->entries);
355         if (res) {
356                 ovl_cache_free(&cache->entries);
357                 kfree(cache);
358                 return ERR_PTR(res);
359         }
360
361         cache->version = ovl_dentry_version_get(dentry);
362         ovl_set_dir_cache(dentry, cache);
363
364         return cache;
365 }
366
367 static int ovl_iterate(struct file *file, struct dir_context *ctx)
368 {
369         struct ovl_dir_file *od = file->private_data;
370         struct dentry *dentry = file->f_path.dentry;
371
372         if (!ctx->pos)
373                 ovl_dir_reset(file);
374
375         if (od->is_real)
376                 return iterate_dir(od->realfile, ctx);
377
378         if (!od->cache) {
379                 struct ovl_dir_cache *cache;
380
381                 cache = ovl_cache_get(dentry);
382                 if (IS_ERR(cache))
383                         return PTR_ERR(cache);
384
385                 od->cache = cache;
386                 ovl_seek_cursor(od, ctx->pos);
387         }
388
389         while (od->cursor.l_node.next != &od->cache->entries) {
390                 struct ovl_cache_entry *p;
391
392                 p = list_entry(od->cursor.l_node.next, struct ovl_cache_entry, l_node);
393                 /* Skip cursors */
394                 if (p->name) {
395                         if (!p->is_whiteout) {
396                                 if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
397                                         break;
398                         }
399                         ctx->pos++;
400                 }
401                 list_move(&od->cursor.l_node, &p->l_node);
402         }
403         return 0;
404 }
405
406 static loff_t ovl_dir_llseek(struct file *file, loff_t offset, int origin)
407 {
408         loff_t res;
409         struct ovl_dir_file *od = file->private_data;
410
411         mutex_lock(&file_inode(file)->i_mutex);
412         if (!file->f_pos)
413                 ovl_dir_reset(file);
414
415         if (od->is_real) {
416                 res = vfs_llseek(od->realfile, offset, origin);
417                 file->f_pos = od->realfile->f_pos;
418         } else {
419                 res = -EINVAL;
420
421                 switch (origin) {
422                 case SEEK_CUR:
423                         offset += file->f_pos;
424                         break;
425                 case SEEK_SET:
426                         break;
427                 default:
428                         goto out_unlock;
429                 }
430                 if (offset < 0)
431                         goto out_unlock;
432
433                 if (offset != file->f_pos) {
434                         file->f_pos = offset;
435                         if (od->cache)
436                                 ovl_seek_cursor(od, offset);
437                 }
438                 res = offset;
439         }
440 out_unlock:
441         mutex_unlock(&file_inode(file)->i_mutex);
442
443         return res;
444 }
445
446 static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
447                          int datasync)
448 {
449         struct ovl_dir_file *od = file->private_data;
450         struct dentry *dentry = file->f_path.dentry;
451         struct file *realfile = od->realfile;
452
453         /*
454          * Need to check if we started out being a lower dir, but got copied up
455          */
456         if (!od->is_upper && ovl_path_type(dentry) == OVL_PATH_MERGE) {
457                 struct inode *inode = file_inode(file);
458
459                 realfile = od->upperfile;
460                 if (!realfile) {
461                         struct path upperpath;
462
463                         ovl_path_upper(dentry, &upperpath);
464                         realfile = ovl_path_open(&upperpath, O_RDONLY);
465                         mutex_lock(&inode->i_mutex);
466                         if (!od->upperfile) {
467                                 if (IS_ERR(realfile)) {
468                                         mutex_unlock(&inode->i_mutex);
469                                         return PTR_ERR(realfile);
470                                 }
471                                 od->upperfile = realfile;
472                         } else {
473                                 /* somebody has beaten us to it */
474                                 if (!IS_ERR(realfile))
475                                         fput(realfile);
476                                 realfile = od->upperfile;
477                         }
478                         mutex_unlock(&inode->i_mutex);
479                 }
480         }
481
482         return vfs_fsync_range(realfile, start, end, datasync);
483 }
484
485 static int ovl_dir_release(struct inode *inode, struct file *file)
486 {
487         struct ovl_dir_file *od = file->private_data;
488
489         if (od->cache) {
490                 mutex_lock(&inode->i_mutex);
491                 ovl_cache_put(od, file->f_path.dentry);
492                 mutex_unlock(&inode->i_mutex);
493         }
494         fput(od->realfile);
495         if (od->upperfile)
496                 fput(od->upperfile);
497         kfree(od);
498
499         return 0;
500 }
501
502 static int ovl_dir_open(struct inode *inode, struct file *file)
503 {
504         struct path realpath;
505         struct file *realfile;
506         struct ovl_dir_file *od;
507         enum ovl_path_type type;
508
509         od = kzalloc(sizeof(struct ovl_dir_file), GFP_KERNEL);
510         if (!od)
511                 return -ENOMEM;
512
513         type = ovl_path_real(file->f_path.dentry, &realpath);
514         realfile = ovl_path_open(&realpath, file->f_flags);
515         if (IS_ERR(realfile)) {
516                 kfree(od);
517                 return PTR_ERR(realfile);
518         }
519         INIT_LIST_HEAD(&od->cursor.l_node);
520         od->realfile = realfile;
521         od->is_real = (type != OVL_PATH_MERGE);
522         od->is_upper = (type != OVL_PATH_LOWER);
523         file->private_data = od;
524
525         return 0;
526 }
527
528 const struct file_operations ovl_dir_operations = {
529         .read           = generic_read_dir,
530         .open           = ovl_dir_open,
531         .iterate        = ovl_iterate,
532         .llseek         = ovl_dir_llseek,
533         .fsync          = ovl_dir_fsync,
534         .release        = ovl_dir_release,
535 };
536
537 int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
538 {
539         int err;
540         struct path lowerpath;
541         struct path upperpath;
542         struct ovl_cache_entry *p;
543
544         ovl_path_upper(dentry, &upperpath);
545         ovl_path_lower(dentry, &lowerpath);
546
547         err = ovl_dir_read_merged(&upperpath, &lowerpath, list);
548         if (err)
549                 return err;
550
551         err = 0;
552
553         list_for_each_entry(p, list, l_node) {
554                 if (p->is_whiteout)
555                         continue;
556
557                 if (p->name[0] == '.') {
558                         if (p->len == 1)
559                                 continue;
560                         if (p->len == 2 && p->name[1] == '.')
561                                 continue;
562                 }
563                 err = -ENOTEMPTY;
564                 break;
565         }
566
567         return err;
568 }
569
570 void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list)
571 {
572         struct ovl_cache_entry *p;
573
574         mutex_lock_nested(&upper->d_inode->i_mutex, I_MUTEX_PARENT);
575         list_for_each_entry(p, list, l_node) {
576                 struct dentry *dentry;
577
578                 if (!p->is_whiteout)
579                         continue;
580
581                 dentry = lookup_one_len(p->name, upper, p->len);
582                 if (IS_ERR(dentry)) {
583                         pr_err("overlayfs: lookup '%s/%.*s' failed (%i)\n",
584                                upper->d_name.name, p->len, p->name,
585                                (int) PTR_ERR(dentry));
586                         continue;
587                 }
588                 ovl_cleanup(upper->d_inode, dentry);
589                 dput(dentry);
590         }
591         mutex_unlock(&upper->d_inode->i_mutex);
592 }